In particular, the present invention relates to an extrusion head of the type comprising a number of shaped plates, a wire or ply reinforcement guiding device and a die. When packed together, said plates define an intermediate guide duct for reinforcing wires, and two supply ducts for extruded elastomeric material located on opposite sides of the guide duct, and provide for locking together the wire guiding device and the die.
Known extrusion heads of the aforementioned type normally comprise a pack of four plates, the middle two of which define the intermediate guide duct and two cavities respectively housing the wire guiding device and die, which are kept a given distance apart so as to define an upper and lower passage between the die inlet and the two ducts supplying the elastomeric material.
The major drawback of such an arrangement is that the wire guiding device and die, the mutual position of which determines the geometrical characteristics of the tread plies, present separate connecting points or shoulders and are not directly connected. Consequently, differing wear on the shoulders results in a corresponding variation in the mutual position of the wire guiding device and die and in the characteristics of the tread plies.